Conventionally, a throttle control apparatus includes a motor control unit (throttle position control unit) for controlling electricity supplied to an electric motor so as to manipulate a valve member relative to a housing in a fluid control valve.
According to EP 1426589 A2 (JP-A-2004-169614), an exhaust gas recirculation apparatus (EGR apparatus) is disclosed as an example of a fluid control valve. An internal combustion engine discharges exhaust gas from a combustion chamber thereof, and the EGR apparatus recirculates the exhaust gas as EGR gas partially into an air intake pipe of the engine. An exhaust gas recirculation valve (EGR valve) is provided midway through an exhaust gas recirculation pipe (EGR pipe) of the exhaust gas recirculation apparatus (EGR apparatus). The electric motor produces driving force to manipulate the butterfly valve so as to rotate the butterfly valve in a control range between a full close position and a full open position. Thus, the butterfly valve serves as an electric EGR valve to control an amount of EGR gas recirculated into the intake pipe, which communicates with the combustion chamber of the engine.
The throttle control apparatus includes an electric motor serving as a power source for controlling the butterfly valve. The throttle control apparatus further includes reduction gears serving as a transmission device to control rotation speed of a motor shaft of the electric motor at a predetermined gear ratio by performing two-stage gear reduction. The reduction gears increase driving force of the electric motor transmitted to the valve shaft of the butterfly valve. The reduction gears are constructed of first to third gears. The first gear is fixed to the motor shaft of the electric motor for rotating around the axis of the motor shaft. The second gear serves as an intermediate reduction gear rotative around the axis of a gear shaft press-inserted into the housing. The third gear serves as a valve gear fixed to a valve shaft of the butterfly valve rotative around the axis of the valve shaft. The intermediate gear is integrated with a large diameter gear, which is geared with the motor gear, and a small diameter, which is geared with the valve gear.
In the EGR valve disclosed in EP 1426589 A2, a return spring is provided between the valve gear and the housing to bias the butterfly valve in the close rotative direction relative to the valve gear. In this structure, when electricity supply to the electric motor is terminated, the return spring applies biasing force to the valve gear, thereby rotating the valve gear in the close rotative direction. Thus, the butterfly valve, which is connected with the valve gear via the valve shaft, is returned to the full close position.
In the EGR valve disclosed in EP 1426589 A2, the outer circumferential periphery of the butterfly valve defines an annular seal ring groove provided with a C-shaped seal ring for reducing leakage of EGR gas when the butterfly valve rotates in the close rotative direction. In this structure, tension works to radially expand the seal ring, so that a gap between the outer circumferential periphery of the butterfly valve and the wall surface defining the fluid passage in the housing is sealed as the butterfly valve rotates in the close rotative direction toward the full close position.
In this structure, electricity supply to the electric motor is terminated when a full close control is performed to manipulate the butterfly valve to be in the full close position. In this operation, the butterfly valve is returned to the full close portion by being applied with the biasing force of the return spring. In general, gears define a predetermined backlash therebetween so that gears are smoothly movable in the structure of the reduction gears. In a condition where the butterfly valve is maintained in the full close position by being applied with the biasing force of the return spring, the motor gear and the intermediate gear may rattle due to a gap (backlash) between surfaces via which the motor gear is in contact with the intermediate gear. In addition, in this condition, the intermediate gear and the valve gear may rattle due to the gap (backlash) between surfaces via which the intermediate gear is in contact with the valve gear.
In particular, the vehicle and the engine may drastically vibrate when the vehicle is operated at high speed or when high road is imposed on the engine. In this condition, vibration of the vehicle and/or the engine may be transmitted to the housing, and consequently, the first to third gear, i.e., the motor gear, the intermediate gear, and the valve gear may drastically vibrate. When the motor gear and the intermediate gear vibrate, the surfaces of the motor gear and the intermediate gear repeat collision and ablation therebetween. As a result, the surfaces of the motor gear and the intermediate gear may abnormally abrade away. When the intermediate gear and the valve gear vibrate, the surfaces of the intermediate gear and the valve gear repeat collision and ablation therebetween. As a result, the surfaces of the intermediate gear and the valve gear may abnormally abrade away.
As a result, when the butterfly valve is rotated to the open rotative direction by utilizing the driving force of the electric motor, the motor gear and the intermediate gear may insufficiently mesh with each other. Consequently, the motor gear may spin with respect to the intermediate gear, or the motor gear may be stack to the intermediate gear. In addition, the intermediate gear and the valve gear may insufficiently mesh with each other, consequently, the intermediate gear may spin with respect to the valve gear, or the intermediate gear may be stack to the valve gear. Accordingly, in the EGR valve disclosed in EP 1426589 A2, the reduction gears may not sufficiently transmit power, consequently, the butterfly valve may not be properly operated.